1. Field of the Invention
The present invention relates to a method and apparatus for wire-cut electrical discharge machining and particularly to a method and apparatus for handling a core formed by cutting a workpiece into a contour shape.
2. Description of the Background Art
FIG. 19 is a conventional wire-cut electrical discharge machining apparatus described in Japanese Laid-Open Patent Publication No. 57-201127, wherein a workpiece 1 is machined by a wire electrode (hereinafter referred to as the "wire 2"). An upper nozzle 3 locates the wire 2 above the workpiece 1, and a lower nozzle 4 locates the wire 2 under the workpiece 1. As a result of the machining of a core which is to be cut off from the workpiece 1 by the wire 2, a machined groove 6 is formed between the workpiece 1 and a core 5. A bridging member 10 which spans the machined groove 6 is used to keep the core 5 unseparated from the workpiece 1. A bridging device 11 is used to transfer the bridging member 10.
In operation, a voltage is applied between the workpiece 1 and the wire 2 by a machining power supply, not shown, and generates a discharge. The wire 2 is positioned proximate to the workpiece 1 by the upper nozzle 3 and the lower nozzle 4. The workpiece 1 and the wire 2 are moved relative to each other under a command from an NC apparatus, not shown, to cut the workpiece 1 into a predetermined contour shape, whereby the core 5 is formed as the groove 6 is machined between the core 5 and the workpiece 1. Immediately before cutting off is complete, machining is stopped once and the bridging device 11 is activated to bond the bridging member 10 to the core 5 and the workpiece 1 across the machined groove 6. After the bridging is secure, the "portion left for cutting" is machined.
The conventional electrical discharge machining apparatus constructed as described above has a problem that the core may tip or shift after cutting, depending on the shape and/or size of the core 5 or the fitting method of the bridging members 10.
Also, the conventional electrical discharge machining apparatus has a problem that when multiple cores are to be removed from one workpiece 1, the bridging member 10 will interfere with an adjacent machining area especially when the cores 5 are small, disallowing next machining. Further, if the bridging member 10 has been arranged to prevent interference, the number of cores removable from the workpiece 1 will be smaller, resulting in lower efficiency.
Another problem faced by the conventional electrical discharge machining apparatus is that the bridging member 10 may interfere with the upper nozzle 3 depending on the size of the core 5 or the size or fitting positions of the bridging members 10.
A related problem is that finishing cannot be performed efficiently.